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Bad running after new head gasket - cause?

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Old Aug 22nd, 2013, 13:41   #11
Laird Scooby
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Just a suggestion here from an experience i had with mine recently. Although the cam timing is correct, is the cam belt tension correct? If it's not quite tight enough it will allow the timing to "wander" causing flat spots, might be worth checking before delving too deeply into electrical gremlins. Not sure on yours if the ignition timing is adjustable, could be they set the timing without getting it properly warm in which case the cold start advance (if it has it, my 740 does) might still be operating resulting in apparently correctly set ignition timing but once warm it is several degrees retarded.
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Old Aug 22nd, 2013, 21:52   #12
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Default I'll pass it on

I'll pass it on to give the garage something to keep it out of mischief. I won't ahve a chance to build the reader until next week.
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Old Aug 27th, 2013, 08:47   #13
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Default Bits arriving

I should get teh electronic bits to build teh code reader today!
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Old Aug 27th, 2013, 09:57   #14
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Nice one! Any chance you could post a link to where the instructions are for the OBD reader please? I'm guessing they're on here somewhere but not sure where to start looking!

On another note, i've just re-read the thread and it seems i missed your post about not being able to get hold of a 1k8 (1.8k) resistor. You're right, it is a preferred value and i had no trouble finding it listed by the supplier i use - Spiratronics 1k8 resistor - they do other variants of that value as well (higher/lower power, construction etc) and they also do a wide range of toggle switches too. I've been using them for 2-3 years now and generally speaking they are cheaper than most other places (much cheaper than Maplins most of the time!), have very good customer service and sensible delivery charges. For example i bought a mixture of bits a month or two back (resistors, LEDs, capacitors, heat shrink sleeving, USB sockets etc) that came to about 15 for the components and the P&P was just 1.49.

If you tinker with electronics as a hobby (as i do, it was my career once until redundancy) then Spiratronics are well worth adding to your bookmarks. Granted they can't get everything but i've seen their range grow in the time i've known them so maybe one day they will have everything you could possibly imagine!
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Old Aug 27th, 2013, 11:09   #15
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Default Main "article" on box

Main article on box here - http://www.volvoforums.org.uk/showthread.php?t=61562


More here - and don't forget to click through the links to the further resources -

http://www.volvoforums.org.uk/showthread.php?t=186499

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Old Sep 2nd, 2013, 08:57   #16
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Default Progress?

Well, the box is built and with the garage.

Meanwhile, the garage thinks it may have found the problem - low fuel pressure. Fuel pressure is 2 bar not as it apparently should be 4 bar.

Any views?
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Old Sep 2nd, 2013, 11:42   #17
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I'm not sure so i'm assuming (not always a good thing!) yours is a 940 with the B230FT engine?

Having looked at my main source of reference for cars i either don't know or don't have a Haynes or genuine WSM for, it appears the normal (unregulated) fuel pressure is 3.5 bar, regulated to approx 2 bar with the engine running.

Based simply on that evidence, i don't see that only having 2 bar to start with is going to cause major problems all the time. It could be something as simple as a blocked fuel filter, lazy pump or similar or possibly a dodgy fuel pressure regulator.
Before you proceed any furtherr, i would ask the garage to clarify whether they tested the fuel pressure with the engine running or not, if it was running, was the vacuum hose connected to the fuel pressure reg and did they take the reading from before or after the FPR.

Not being negative but it sounds a little like he's thrown you a red herring to buy himself time to fiddle and try and find the fault or an excuse to fit something you don't need in the hope it will fix the problem.
Could also be worth consulting the Haynes book for your car and/or a Volvo dealer for clarification on the correct fuel pressure readings.
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Old Sep 2nd, 2013, 12:33   #18
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Default Honest

There is no doubt that he is a totally honest man - there is no way he would dishonestly buy time. And the huge flat spot, now that fuel pressure has been mentioned, could very well be redolent of a fuelling problem. Further, there is no time pressure as I have two other Volvos to toodle about in, a B234F (who is rapidly coming up for the need for an exhaust - I think I might treat her to a Jetex stainless) and a 765T. But I will have a quick look in my Haynes manual, thanks.

Against the fuelling theory - she passed the MoT on Sat, so if the fuel pressure was way off, how could the emissions have been right?
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Old Sep 2nd, 2013, 12:56   #19
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His honesty isn't what i was questioning, i've just known a few garages to say something that sounds good/technical to gain some time to find the fault, in fact in many garages it's common practice, especially on a job where the final fix doesn't justify umpteen hours of labour to find the fault fixed with a 50p part.

I always thought Jetex were heavy duty aluminised mild steel? I've been looking at an OBX Racing stainless steel exhaust. I'm sure they do one for the B234 engine as well. Although it has to come from the USA, with the exchange rate etc it still works out cheaper than Jetex and if i've linked to the correct seller they will ship to the UK (quoted me about $160 to ship a pair of V6 manifolds and de-cat pipe, reckon a Volvo system would be about the same) so might be worth considering as an option?

I wonder if your car would still have passed the emissions test with a higher fuel pressure? Fuel injected (mixture) is a function of fuel pressure and injector time so the higher the fuel pressure, the richer the mixture for any given injection time. Likewise the injector time could be extended by the ECU to compensate for low pressure but that would only extend so far until fuel starvation problems show up.
As you have probably worked out, as manifold pressure changes the fuel pressure should alter as well. If your pump can only provide 2bar max pressure on the unregulated side then there could well be a problem there.
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Old Sep 2nd, 2013, 14:12   #20
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Default Haynes tacet

Haynes appears to be wholly silent on the issue of the right fuel pressure.
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